Disc filter sector

ABSTRACT

A disc filter (and disc filter constructed from a number of sectors) includes a filter member and a supporting structure. The supporting structure is formed by two opposed perforated plates which each have at least about 70% flat supporting portions which separate recess portions (which typically extend radially). The recess portions of each plate are welded to either supporting portions or recess portions of the other plate.

CROSS REFERENCE TO RELATED APPLICATION

This application is the U. S. National Phase of PCT/F194/00111 filedMar. 28, 1994.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a disc filter sector. The disc filtersector in accordance with the present invention is especially suitablefor both wood processing and mining industry.

A disc filter is an apparatus used in both wood processing and miningindustry primarily for thickening materials. The filter most usuallycomprises a number of discs which are arranged on a horizontal shaft,and the surface of which is made liquid-permeable. The discs of thefilter are arranged in a vat rotatably around their axis so that atleast a half of the disc surfaces is submerged in the vat in thematerial to filtered. Said discs are formed of a number of so calledsectors next to each other having their inner ends connected to theshaft so that the liquid that has passed the sector surface is allowedto flow from the inside of the sector through the shaft out from theapparatus. The surface of the sectors may be made either of cloth,plastics or metal wire or even of a perforated plate. If a wire is usedthe sector requires a special supporting structure, which keeps theflexible and elastic wire in shape. Almost an innumerable amount ofdifferent technical solutions are possible in the supporting structureof the sector. For example, the use of different wooden or plasticprofiles as supporting structures is known.

Swedish patent 79654 illustrates a sector structure, which has a platesubstantially undulating in V-shape, in which plate the undulations areparallel. U.S. Pat. No. 3,948,779 disclose a supporting structure forthe sector, which is also undulating in V-shape, but the undulations inthis arrangement are radial. WO publication 87/04640 also illustrates asector structure having V-shaped radial undulations. Further, alsopublished Swedish patent application 465 658 discloses a supportingstructure with V-shaped undulations. It is a characterizing featureof-all above described structures that the filtering surface of thesector is supported against the ridge of the undulated plate, wherebythe pressure differences between the outer and inner surface of thesector, especially at high pressures of the washing liquid, of course,tend to press the wire surface to the groove between the ridges.Moreover, the bending stiffness parallel to the rim of such an undulatedsector is very weak, especially when the supporting structure is simple.

The above mentioned US and WO publications as well as U.S. Pat. No.-2781,133 also each methods of making the supporting structure of thesector rigid parallel to the rim, for example, by arranging twoundulated plates opposite to each other or by attaching supporting ribsor like parallel to the rim of the undulated plates. The positioning ofsuch supporting ribs and finding appropriate welding surfaces makes themanufacture of the sector complicated and risky.

The object of the present invention is to facilitate the manufacture ofthe filter sector and to simplify the structure thereof. If, forexample, a sector in accordance with the present invention ismanufactured by welding, the amount of the necessary welding spotsdiminishes at least to half of the previous- Further, an object of thepresent invention is to bring about a sector having a high bendingstiffness. Yet another object of the present invention is to bring abouta sector, which is highly supporting to the wire.

The characteristic features of a disc filter sector fulfilling theobjects of the present invention become apparent in the accompanyingpatent claims.

Advantages of a sector of the present invention compared with thesectors in accordance with prior art are, for example, the following:

a sturdy box structure, in which separate supporting ribs inside thesector are not necessary;

it supports the wire well;

separate flow channels for the filtrate, i.e. a small flow resistance;

the filtrate volume may be minimized allowing a possibility to optimizethe whole operation of the filter apparatus;

smaller need of material, lighter, easier to manufacture, less welding,minimized plate thickness compared to a conventional perforated platesector;

it is easy to arrange the "conicity" of the sector towards the inner endby means of undulations, the part closer to the shaft being thicker thanthe part further apart, whereby the cross-sectional flow area remainsconstant throughout the entire sector;

90% of the through-washability remains; and

the sector is formed of identical halves, which further facilitates themanufacture of the sector.

BRIEF DESCRIPTION OF THE DRAWING

The invention is further described below, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a disc filter in accordance with theprior art;

FIG. 2 schematically illustrates a disc of the disc filter;

FIG. 3 schematically illustrates a sector of a disc filter in accordancewith the present invention;

FIG. 4 schematically illustrates a preferred embodiment of the presentinvention as a sectional view along line A--A in FIG. 3;

FIG. 5 schematically illustrates a preferred embodiment of the presentinvention as a sectional view along line B--B in FIG. 3; and

FIG. 6 schematically illustrates another embodiment of the presentinvention as a sectional view along line A-A in FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

According to FIGS. 1 and 2 a disc filter 10 comprises a vat 12 having ashaft 14 mounted with bearings at the ends thereof. Said shaft 14 isprovided with a number of filter discs 16. Means 18 are arranged betweenthe discs 16 for removing the filtered cake from the apparatus. At leastone end of the shaft 14 is provided with means 20 for removing thefiltrate from the inside of the shaft 14. Discs 16 comprise sectors 22,the interior of which is connected to the interior of the shaft 14 bymeans of flow opening 24, through which the filtrate flows from thesector 22 to the inside of the shaft 14. The sector 22 is covered by awire cloth 26 or like.

FIG. 3 schematically illustrates a sector 22 of the disc filter inaccordance with a preferred embodiment of the present invention andFIGS. 4 and 5 especially illustrate the supporting structure thereof.The outer end 0 (higher in the drawing) of the sector 22 issubstantially parallel to the rim of the disc and it also substantiallyjoins the rim of the disc. It is, of course, possible that in some casesthe outer end 0 may not be curved but also, for example due tomanufacturing reasons, straight. The inner end I (at the bottom in thedrawing) of the sector is usually straight, but it may also be curved.Further, the direction of the perpendicular drawn to the inner end Imay, if desired, deviate from the direction of the center line of thesector. The inner end I of each sector 22 is provided with a flowchannel (not shown), by means of which the hollow interior of the sectoris connected to the filtrate discharge channels (not shown) arrangedinto connection with the shaft of the filter. A preferred embodiment ofthe sector 22 comprises, according to FIGS. 4 and 5, two opposedperforated plate elements 30 and 32 attached, for example, by welding toeach other, and a filter member 34 (shown only in FIG. 4), preferably aplastic sleeve or metal wire, is stretched over the surface of theplate. The perforated plate elements 30 and 32 are waved according tothe drawings so that there is a relatively long portion 38 parallel tothe surface of the sector between two adjacent recesses 36. The recessesof the opposed perforated plate elements 30 and 32 are arranged in thisembodiment to alternate so that a recess 36 of the first plate 30 issupported by a part 38 of the plate 32. This results in a goodsupporting surface to the wire with as little need as possible to bendthe perforated plate. By attaching the perforated plate elements 30 and32 to each other of the bottom of the recesses 36 a sturdy box structureis obtained, which effectively resists both axially directed forcestending to bend the sector in a radial plane and axially directed forcestending to bend the sector in a plane tangential o the rim. At least70of the surface of each perforated plate element 30, 32 must form thesurface part 38 parallel to the wire, in other words the wire 34 issupported of at least 70% of the surface area thereof. At least the part38 of the surface of each perforated plate element parallel to said wiremust be perforated, but preferably the plate elements 30 and 32 areperforated throughout their entire area. FIGS. 4 and 5 also illustrate,how the dimension of the sector parallel to the shaft of the filterincreases when moving from the outer rim inwards (sections A--A and B--Bin FIG. 3). By this arrangement it is possible to increase thecross-sectional flow area to correspond to the increasing amount of thefiltrate to be moved.

FIG. 6 illustrates a second embodiment of a sector of the disc filter inaccordance with the present invention, in which the recesses 36' of theperforated plates 30' and 32' are arranged to face each other and theplates 30' and 32' are thus attached to each other of the bottom of theopposed recesses 36'.

It is a characterizing feature of all shown embodiments that therecesses of each sector are radial as shown in FIG. 3. The recesses may,however, be, for example, parallel in each sector, if the manufacturingtechnique or the operation of the sector such requires.

As becomes apparent from the above description, a filter sector inaccordance with the present invention is very simple to manufacture. Itresults, however, in a structure that at least corresponds in strengthto the prior art sectors. It must be noted that the present invention isillustrated above with references to two exemplary embodiments. Saidexamples are given only to exemplify, not to restrict the invention, butthe inventive concept may be applied to many other structures. Thus thepresent invention is defined merely by the accompanying patent claims.

I claim:
 1. A disc filter sector comprising:a filter member; and asupporting structure for said filter member; said supporting structurecomprising two opposed perforated plate elements each consisting of aplurality of substantially flat supporting portions substantiallyparallel to said filter member and engaging said filter member, and aplurality of recess portions spaced from each other by said supportingportions and not engaging said filter member, recess portions of each ofsaid opposed plate elements engaging a portion of the other of saidopposed plate elements.
 2. A disc filter sector as recited in claim 1wherein each of said plate elements has a surface area, and wherein atleast 70% of the surface area of each of said plate elements comprisessaid substantially flat supporting portions.
 3. A disc filter sector asrecited in claim 2 wherein recess portions of each of said opposed plateelements engages and is attached to recess portions of the other of saidopposed plate elements.
 4. A disc filter sector as recited in claim 2wherein recess portions of each of said opposed plate elements engagesand is attached to supporting portions of the other of said opposedplate elements.
 5. A disc filter sector as recited in claim 3 whereinportions of said opposed plate elements are attached to each other bywelding.
 6. A disc filter sector as recited in claim 4 wherein portionsof said opposed plate elements are attached to each other by welding. 7.A disc filter sector as recited in claim 1 wherein said recess portionsextend in a substantially radial direction.
 8. A disc filter sector asrecited in claim 1 wherein said sector includes an outer end and aninner end, said sector having a greater width at said outer end than atsaid inner end.
 9. A disc filter sector as recited in claim 1 whereinrecess portions of each of said opposed plate elements engages and isattached to recess portions of the other of said opposed plate elements.10. A disc filter sector as recited in claim 1 wherein recess portionsof each of said opposed plate elements engages and is attached tosupporting portions of the other of said opposed plate elements.
 11. Adisc filter sector as recited in claim 9 wherein portions of saidopposed plate elements are attached to each other by welding.
 12. A discfilter sector as recited in claim 10 wherein portions of said opposedplate elements are attached to each other by welding.
 13. A disc filtersector as recited in claim 9 wherein said recess portions extend in asubstantially radial direction.
 14. A disc filter sector as recited inclaim 10 wherein said recess portions extend in a substantially radialdirection.
 15. A disc filter sector as recited in claim 1 wherein eachof said opposed plate elements have side edges with inwardly bentportions which engage inwardly bent portions of the other of saidopposed plate elements; and wherein engaging portions of said opposedplate elements are attached to each other by welding.
 16. A disc filtersector as recited in claim 1 including an inner end and an outer end;and in combination with a plurality of other disc filter sectors so asto form a disc filter connected at said inner ends of said sectors to aperforated shaft, liquid flowing through said filter members flowingbetween said opposed plate elements into said perforated shaft.
 17. Adisc filter sector as recited in claim 1 wherein said plate elementshave an outer rim; and wherein engaging portions of said opposed plateelements comprise means for effectively resisting both axially directedforces tending to bend said sector in a plane tangential to said rim,and in a radial plane.
 18. A disc filter sector as recited in claim 9wherein said plate elements have an outer rim; and wherein attachedengaging portions of said opposed plate elements comprise means foreffectively resisting both axially directed forces tending to bend saidsector in a plane tangential to said rim, and in a radial plane.
 19. Adisc filter sector as recited in claim 10 wherein said plate elementshave an outer rim; and wherein attached engaging portions of saidopposed plate elements comprise means for effectively resisting bothaxially directed forces tending to bend said sector in a planetangential to said rim, and in a radial plane.
 20. A disc filter sectorcomprising:a filter member; and a supporting structure for said filtermember; said supporting structure comprising two opposed perforatedplates each comprising a plurality of substantially flat supportingportions engaging and supporting said filter member, and a plurality ofrecess portions spaced from each other by said supporting portions andnot engaging said filter member, said recess portions of each of saidopposed plates engaging and attached to said substantially flatsupporting portions of the other of said plates.
 21. A disc filtersector comprising:a filter member; and a supporting structure for saidfilter member; said supporting structure comprising two opposedperforated plate elements each consisting of a plurality of supportingportions engaging said filter member, and a plurality of recess portionsspaced from each other by said supporting portions and not engaging saidfilter member, recess portions of each of said opposed plate elementsengaging a portion of the other of said opposed plate elements; andwherein each of said plate elements has a surface area, and wherein atleast 70% of the surface area of each of said plate elements comprisessaid supporting portions.